75 Gallon Tank Corys not doing well, Not eating after Gravel change

Hello everyone this is my first post on here, looking to get some advise. I may have messed up, so I have a 75g tank that was well established, has/d 14 neon tetras, 3 female bettas, 1 male beta, 1 albino common pleco (~5”) and 3 albino corys.
( 5 black tetras, 3 albino corys added at time of gravel change)

I changed the substrate to a softer gravel ( other gravel was sharp and was afraid of it hurting the corys over time) I took all the fish out and put them in a different bare tank while I took about 3/4 of the gravel out and changed it to the new gravel ( changed water too)
put everyone back in ~ 2 hours, they had a heater and air stone in the other tank and it was water from the established tank.

I’ve had all of these fish for 6 months and never had any problems with aggression or territory issues, well 1 day later 12 neons,2 black tetras have died, one of my females seems she’s getting close. and the corys have been sitting at the bottom even the ones that were lively before. I’m worried for my Corey’s as they are my favorite fish in the tank.

please don’t hound me on the substrate change, I know about the bacteria, I have mesh bags full of the old gravel around my tank to try and help with the bacteria exchange, the water parameters are perfect and I’m starting to get worried, the corys won’t eat anything I put in there and this is going on day 3 please help if you can!!

 

In moving the fish from tank to tank and removing some of the established bacteria you may have shocked the fish. Not sure if you did temp matching and floated the fish before moving them to the new tank, but all new water could have been slightly different than the previous water. Neons really like a very established mature tank so I am not surprised they died after a big change like that. I would give the corys more time. They can hide when stressed and wont really eat when stressed. You could try some bloodworms to see if they go for a higher valued food. When testing the water try to get water from just above the substrate to make sure that any ammonia or nitrites aren't sitting low where they like to hang out.

 

Would you mind filling out the Emergency Template to help us gain a better understanding of your situation please?

 

Test the water fir ammonia and nitrites.

 

Would you mind filling out the Emergency Template to help us gain a better understanding of your situation please?

I will do this when i get home today, thank you!

Test the water fir ammonia and nitrites.

I did they are ok I will post exact numbers when I get home

In moving the fish from tank to tank and removing some of the established bacteria you may have shocked the fish. Not sure if you did temp matching and floated the fish before moving them to the new tank, but all new water could have been slightly different than the previous water. Neons really like a very established mature tank so I am not surprised they died after a big change like that. I would give the corys more time. They can hide when stressed and wont really eat when stressed. You could try some bloodworms to see if they go for a higher valued food. When testing the water try to get water from just above the substrate to make sure that any ammonia or nitrites aren't sitting low where they like to hang out.

The temperature was exactly the same 79.4, and I have been testing levels everyday when I get home from work, 1 neon has survived and 3 of the black tetras, corys are still laying as of this morning, pleco is fine, bettas are fine besides the one I thought was stressed and not doing well I think she’s hiding, I will post exact levels when I get home with pictures

 

There may be other difference that were not accounted for. You said you have bags of the old substrates so that’s good but maybe place the bags in your hob filters if you have that or place them in the canisters or above the sponge filters so water current can pass through them. I would just wait it out and let everything settle. Clearly it’s environmental stresses and not a pathogen that’s causing problems here. Cories are tough.

 

There may be other difference that were not accounted for. You said you have bags of the old substrates so that’s good but maybe place the bags in your hob filters if you have that or place them in the canisters or above the sponge filters so water current can pass through them. I would just wait it out and let everything settle. Clearly it’s environmental stresses and not a pathogen that’s causing problems here. Cories are tough.

Yes I have 3 bags on top of a 90g sponge filter and others in my hob as well as on top of air stones, trying to do as much as I can, when I get home I’ll post updates and specific readings

 

Would you mind filling out the Emergency Template to help us gain a better understanding of your situation please?

Tank
What is the water volume of the tank? 75g
How long has the tank been running?6months
Does it have a filter? Yes hob emperor 375
Does it have a heater? Yes 300w
What is the water temperature? 79.8
What is the entire stocking of this tank? (Please list all fish and inverts.)3 female bettas, 1 male beta, 1 common pleco, 5 albino Corys, 3 black tetras, 1 neon tetra

lost a Cory today ):

Maintenance
How often do you change the water? Weekly
How much of the water do you change?10-20%
What do you use to treat your water?api or top fin water conditioner
Do you vacuum the substrate or just the water? Both

*Parameters - Very Important
Did you cycle your tank before adding fish? Yes,
What do you use to test the water?api master test kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia:0ppm
Nitrite:0ppm
Nitrate:2.5ishppm
pH:between 7.2-7.6

Feeding
How often do you feed your fish? Once daily
How much do you feed your fish? As much as I could see them eat and not waste
What brand of food do you feed your fish?omega one ( beta) api ( corys and pleco) probiotix (tetras)
Do you feed frozen? No
Do you feed freeze-dried foods? No

Illness & Symptoms
How long have you had this fish? Most for 6 months
How long ago did you first notice these symptoms?4 days ago
In a few words, can you explain the symptoms?lazy, not eating
Have you started any treatment for the illness? No
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all? Laying around, not eating, “paler color”

Explain your emergency situation in detail. (Please give a clear explanation of what is going on, include details from the beginning of the illness leading up to now)
Changed the substrate and added 3 corys and 5 black tetras, it was a well established tank and I may have messed it up with switching gravel. Now all corys won’t eat and having problems getting other fish to eat besides beta

 

Thank you! This is very odd, and I'm not sure there would have been problems with ammonia/nitrite/nitrates realizing you have a very understocked tank even before problems came up. Your pH is usually between 7.2-7.6? What kind of substrate did you have and what substrate is there now?

 

It’s a nice big tank for the number of relative small fish…everything test out fine and the only thing is the # of cories to begin with. So don’t beat yourself over the head. Get more cories for your one left, quarantine them if possible and move forward.

 

Thank you! This is very odd, and I'm not sure there would have been problems with ammonia/nitrite/nitrates realizing you have a very understocked tank even before problems came up. Your pH is usually between 7.2-7.6? What kind of substrate did you have and what substrate is there now?

It was gravel from a older tank my father had years ago, I bought some new gravel to have a smoother substrate because the other had some sharp gravel in it and I was scared for the corys

It’s a nice big tank for the number of relative small fish…everything test out fine and the only thing is the # of cories to begin with. So don’t beat yourself over the head. Get more cories for your one left, quarantine them if possible and move forward.

Will note, I might have shocked them with changing the biggest part of their tank, still not eating, so far lost 12 neons, 2 black, 1 beta, and 1 Cory ): but I was kinda expecting it but then again I tried to do everything to not have this happen. Thanks for the reply!!
Thanks everyone for the replies, I’m gonna play it out and see if it gets better, I’m not gonna let this discourage me! I appreciate every one of you! This is my first time on a fish forum and you guys/gals have made it great!! Thank you so much!

 

How much of the water do you change?10-20%

The only thing that stood out to me was that the weekly water changes you do are really very small.
Maybe because of such small water changes your aquarium water was very different to your tap water now.

Thus, by changing the water when doing the gravel change it may have shocked them as they're used to the old water (Tetras being sensitive) and that's what has killed them.

I suppose you will never really know 100%

I hope the deaths stop soon and your tank becomes the happy place it was.

 

The only thing that stood out to me was that the weekly water changes you do are really very small.
Maybe because of such small water changes your aquarium water was very different to your tap water now.

Thus, by changing the water when doing the gravel change it may have shocked them as they're used to the old water (Tetras being sensitive) and that's what has killed them.

I suppose you will never really know 100%

I hope the deaths stop soon and your tank becomes the happy place it was.

I always have done small water changes unless I was doing a deep clean then 30-40% didn’t wanna take too much out a mess with them, I never thought of that though!! Thank you for the input!! I will keep that in mind the next time I do my water service. I’ve been doing it roughly every other day rn because no one is eating and the tetra food sinks into the gravel

 

I have my doubts about it being the small water changes, if your parameters read around the same more or less—especially with such a large tank and very light stock—it's working.

I appreciate your optimism as it is very necessary in this hobby. No matter how experienced you are, there are many variables outside of our controls that could end up in loss, and sometimes we never find out what could have caused it. We just have to keep pushing forward and trying to stay observant and on-top of things to keep our fish happy.

I have some baseless ideas that you could possibly explore:

1. Stress
   I find it hard to believe, but it can never be ruled out. When fish get stressed their immune systems are weakened and they become incredibly vulnerable to anything.
2. A change in the water supply
   I have seen people lose a lot of fish because there was a change in their water supply, like adding more chlorine than usual or something, or perhaps something in the old pipes that contaminated the water supply somewhere along the way. You aren't the only one I've seen experiencing issues when seemingly water parameters seem fine, but unfortunately the normal things we measure aren't the only things to factor in when determining good quality water (which is why some people just opt for R.O. water).
3. kH buffer
   kH is carbonite hardness, a measurement of calcium and magnesium in the water that aligns with pH and gH levels. The lower it is, your pH and gH (general hardness) will likely be lower and could also be subject to swinging, meaning it could drastically change. The higher it is then the more likely your pH and gH will also be higher, and also more stable. Which is why I asked if your pH is usually ~7.4 and what material your new substrate is made of. If you added a calcium-rich substrate, it could potentially buffer your water and thus creating a different enough environment for your fish to become very stressed out. I find that a lot of fish can be sensitive to kH levels, but perhaps moreso South American species such as most tetras.
4. Inadequate water conditioner
   I've never used topfin before, it looks very ordinary but I can't say how effective it is or is not just by looking it up online. It could be possible that it's not effective enough to remove the toxicity of chlorine, chloramine, heavy metals, and such from the water, but it may not have been too noticeable due to the small water changes that you do that the new water was easily diluted into the rest of the tank water. At least not until you made this big change. I use API Stress Coat sometimes, but I would have used what I feel to be a more reliable water conditioner which would be either Seachem Prime or Fritz Complete. However, if you feel that the water conditioners you're using are good then please take what I say with a grain of salt.
5. Introduced toxins
   Similarly to #2, but I am referring to immediately introduced contaminants. Perhaps there was a strange chemical on the new substrate that may not have been rinsed thoroughly (although rare), or something on your hands and/or equipment that got into the water. Whether you didn't wash all the soap off, used sanitizer/lotion/sunscreen, something was sprayed in the air that got into the tank/equipment.

If you haven't already, maybe gently rinse out filter media with old tank water and do 50% water changes two days in a row, and pick up a cycle boosting live bacteria (I like Seachem Stability) to use while doing those big water changes. It might not be ideal, but in case there is a strange contaminant giving your fish a hard time it might help get it out of the tank. I would also recommend looking into getting Seachem Prime or Fritz Complete (they're extremely similar in comparison and from personal use) to help lower the harmful effects of any potential toxins that may be in your water.

 

I have my doubts about it being the small water changes, if your parameters read around the same more or less—especially with such a large tank and very light stock—it's working.

I appreciate your optimism as it is very necessary in this hobby. No matter how experienced you are, there are many variables outside of our controls that could end up in loss, and sometimes we never find out what could have caused it. We just have to keep pushing forward and trying to stay observant and on-top of things to keep our fish happy.

I have some baseless ideas that you could possibly explore:

1. Stress
   I find it hard to believe, but it can never be ruled out. When fish get stressed their immune systems are weakened and they become incredibly vulnerable to anything.
2. A change in the water supply
   I have seen people lose a lot of fish because there was a change in their water supply, like adding more chlorine than usual or something, or perhaps something in the old pipes that contaminated the water supply somewhere along the way. You aren't the only one I've seen experiencing issues when seemingly water parameters seem fine, but unfortunately the normal things we measure aren't the only things to factor in when determining good quality water (which is why some people just opt for R.O. water).
3. kH buffer
   kH is carbonite hardness, a measurement of calcium and magnesium in the water that aligns with pH and gH levels. The lower it is, your pH and gH (general hardness) will likely be lower and could also be subject to swinging, meaning it could drastically change. The higher it is then the more likely your pH and gH will also be higher, and also more stable. Which is why I asked if your pH is usually ~7.4 and what material your new substrate is made of. If you added a calcium-rich substrate, it could potentially buffer your water and thus creating a different enough environment for your fish to become very stressed out. I find that a lot of fish can be sensitive to kH levels, but perhaps moreso South American species such as most tetras.
4. Inadequate water conditioner
   I've never used topfin before, it looks very ordinary but I can't say how effective it is or is not just by looking it up online. It could be possible that it's not effective enough to remove the toxicity of chlorine, chloramine, heavy metals, and such from the water, but it may not have been too noticeable due to the small water changes that you do that the new water was easily diluted into the rest of the tank water. At least not until you made this big change. I use API Stress Coat sometimes, but I would have used what I feel to be a more reliable water conditioner which would be either Seachem Prime or Fritz Complete. However, if you feel that the water conditioners you're using are good then please take what I say with a grain of salt.
5. Introduced toxins
   Similarly to #2, but I am referring to immediately introduced contaminants. Perhaps there was a strange chemical on the new substrate that may not have been rinsed thoroughly (although rare), or something on your hands and/or equipment that got into the water. Whether you didn't wash all the soap off, used sanitizer/lotion/sunscreen, something was sprayed in the air that got into the tank/equipment.

If you haven't already, maybe gently rinse out filter media with old tank water and do 50% water changes two days in a row, and pick up a cycle boosting live bacteria (I like Seachem Stability) to use while doing those big water changes. It might not be ideal, but in case there is a strange contaminant giving your fish a hard time it might help get it out of the tank. I would also recommend looking into getting Seachem Prime or Fritz Complete (they're extremely similar in comparison and from personal use) to help lower the harmful effects of any potential toxins that may be in your water.

1.Thank you for taking the time of your day to type this! I know the tetras were extremely stressed because most of them lost their color and died over night ): I’m down to 1 neon and 3 black.
2.Where I live I have “city” water so it might be constantly changing, I myself do not drink it as I grew up on a well and hate the chlorine taste so I can’t tell you if it’s more or less, I’m sorry.
3. My “city” water has a lot of calcium in it which builds up on the glass, I tend to scrape it off when I do my water changes as it only builds where it evaporated, I’m not sure if I read that part correctly but you said that was good? I’ve never heard of “kh”
4. I use api everything but when I was getting conditioner they were out but I’ve been using this for a pretty long time with no issues at all, I have a 10g shrimp tank that I tend to wait a couple weeks on for the water, they tend to keep it tidy and my plants are doing better now that I put them in that tank (even though there is less light?) I have bout api now but I’m almost through the bottle of the other conditioner so I’m gonna use it up first, also is there a problem with adding to much conditioner? The cap on this one is kinda hard to get correct and I usually put a little extra in, would that be part of the problem? I also put in a little bit of aquarium salt to try and help them, I’ve never done this before so i did a very little amount, about 1/4 of what I was supposed to
5. I always clean up before getting into my tanks because I work in the heavy machinery field so I tend to be very dirty when I get home, I make sure I’m super clean before even feeding them, we recently got one of those automatic air fresheners and it sits relatively close to my tanks because on the other side of my living room we have animals that are sensitive to the smells ( they don’t stink) so maybe that might be it? I’ve watched it spray it doesn’t seem to get high enough to actually get into the tank but I will move it if this might be a problem.
Thank you so much for your time for replying and for reading this long answer, hope you have a good weekend!!

I have my doubts about it being the small water changes, if your parameters read around the same more or less—especially with such a large tank and very light stock—it's working.

I appreciate your optimism as it is very necessary in this hobby. No matter how experienced you are, there are many variables outside of our controls that could end up in loss, and sometimes we never find out what could have caused it. We just have to keep pushing forward and trying to stay observant and on-top of things to keep our fish happy.

I have some baseless ideas that you could possibly explore:

1. Stress
   I find it hard to believe, but it can never be ruled out. When fish get stressed their immune systems are weakened and they become incredibly vulnerable to anything.
2. A change in the water supply
   I have seen people lose a lot of fish because there was a change in their water supply, like adding more chlorine than usual or something, or perhaps something in the old pipes that contaminated the water supply somewhere along the way. You aren't the only one I've seen experiencing issues when seemingly water parameters seem fine, but unfortunately the normal things we measure aren't the only things to factor in when determining good quality water (which is why some people just opt for R.O. water).
3. kH buffer
   kH is carbonite hardness, a measurement of calcium and magnesium in the water that aligns with pH and gH levels. The lower it is, your pH and gH (general hardness) will likely be lower and could also be subject to swinging, meaning it could drastically change. The higher it is then the more likely your pH and gH will also be higher, and also more stable. Which is why I asked if your pH is usually ~7.4 and what material your new substrate is made of. If you added a calcium-rich substrate, it could potentially buffer your water and thus creating a different enough environment for your fish to become very stressed out. I find that a lot of fish can be sensitive to kH levels, but perhaps moreso South American species such as most tetras.
4. Inadequate water conditioner
   I've never used topfin before, it looks very ordinary but I can't say how effective it is or is not just by looking it up online. It could be possible that it's not effective enough to remove the toxicity of chlorine, chloramine, heavy metals, and such from the water, but it may not have been too noticeable due to the small water changes that you do that the new water was easily diluted into the rest of the tank water. At least not until you made this big change. I use API Stress Coat sometimes, but I would have used what I feel to be a more reliable water conditioner which would be either Seachem Prime or Fritz Complete. However, if you feel that the water conditioners you're using are good then please take what I say with a grain of salt.
5. Introduced toxins
   Similarly to #2, but I am referring to immediately introduced contaminants. Perhaps there was a strange chemical on the new substrate that may not have been rinsed thoroughly (although rare), or something on your hands and/or equipment that got into the water. Whether you didn't wash all the soap off, used sanitizer/lotion/sunscreen, something was sprayed in the air that got into the tank/equipment.

If you haven't already, maybe gently rinse out filter media with old tank water and do 50% water changes two days in a row, and pick up a cycle boosting live bacteria (I like Seachem Stability) to use while doing those big water changes. It might not be ideal, but in case there is a strange contaminant giving your fish a hard time it might help get it out of the tank. I would also recommend looking into getting Seachem Prime or Fritz Complete (they're extremely similar in comparison and from personal use) to help lower the harmful effects of any potential toxins that may be in your water.

1.Thank you for taking the time of your day to type this! I know the tetras were extremely stressed because most of them lost their color and died over night ): I’m down to 1 neon and 3 black.
2.Where I live I have “city” water so it might be constantly changing, I myself do not drink it as I grew up on a well and hate the chlorine taste so I can’t tell you if it’s more or less, I’m sorry.
3. My “city” water has a lot of calcium in it which builds up on the glass, I tend to scrape it off when I do my water changes as it only builds where it evaporated, I’m not sure if I read that part correctly but you said that was good? I’ve never heard of “kh”
4. I use api everything but when I was getting conditioner they were out but I’ve been using this for a pretty long time with no issues at all, I have a 10g shrimp tank that I tend to wait a couple weeks on for the water, they tend to keep it tidy and my plants are doing better now that I put them in that tank (even though there is less light?) I have bout api now but I’m almost through the bottle of the other conditioner so I’m gonna use it up first, also is there a problem with adding to much conditioner? The cap on this one is kinda hard to get correct and I usually put a little extra in, would that be part of the problem? I also put in a little bit of aquarium salt to try and help them, I’ve never done this before so i did a very little amount, about 1/4 of what I was supposed to
5. I always clean up before getting into my tanks because I work in the heavy machinery field so I tend to be very dirty when I get home, I make sure I’m super clean before even feeding them, we recently got one of those automatic air fresheners and it sits relatively close to my tanks because on the other side of my living room we have animals that are sensitive to the smells ( they don’t stink) so maybe that might be it? I’ve watched it spray it doesn’t seem to get high enough to actually get into the tank but I will move it if this might be a problem.
Thank you so much for your time for replying and for reading this long answer, hope you have a good weekend!!

Maybe these pictures could help, I noticed the corys are like maybe once a day (that I see) are moving now, the food I put in last night is gone but I don’t know if that was the pleco or not he’s been hiding behind the coral wall, he usually hides in the log but the gravel bag is in there

 

There are good organisms that colonize the gravel substrate of an aquarium, and there are bad things there as well.
A sudden major substrate change has the potential to unleash the bad things that were once buried, such as Columnaris bacteria, even pockets of toxic gases.
Years ago I experienced a similar disaster after a major substrate change. I tried to anticipate any potential problems & took great care to make the transition safe for the fish. Somehow I failed. After the initial fish die off, things returned to normal after a few weeks.
This sort of thing happens to rookie fishkeepers & the experienced. Things will likely level out soon.

 

Hard to say with city water, lots of things can happen whether it's treatment or something in pipes. Even more reason to make sure you have good water conditioner. Which, I think nowadays a little more than the recommended dose of your water conditioner should be harmless. If you spill half a bottle in a tank then that would be different, but I dont think being slightly off with measurement will cause any harm.

KH is definitely an advanced topic in fishkeeping, at least on the water chemistry side of things. I can't consider myself an expert on this topic, as it hasnt been too relevant to my personal tanks. It is rarely if ever mentioned to beginners and on many blogs and websites for keeping aquariums that only share mostly basic information. It only becomes a little more important to know if you plan to keep fish have unique requirements in their water. Like certain rift lake cichlids of Africa prefer high pH and very hardwater, or many south american species that might prefer much more acidic conditions. If there is anything you should take away about kH here, it influences pH. If you have hardwater deposits then you probably have some decent kH that should in theory keep your pH stable. But city water can be weird sometimes...

Salt is pretty handy in the hobby but I personally recommend situational use. Above all else, be sure that when you use it that it is completely diluted in some tank water before you put it into the tank. The salt crystals can be irritating to bottom feeders that come across it, especially any scaleless fish like loaches. It can be useful as a non-medicated treatment against external parasites and infections, however with regular use of salt it could potentially make a salt treatment less effective, a tolerance can be built by external parasites and such. Salt is supposed to stimulate fish into producing a thicker slime coat around their body, and this is supposed to help them better fight off any potential infections while theyre stressed. API Stresscoat does this and helps condition the water as well, but I think with a less irritating ingredient than salt (aloe I think?). If your fish get stressed a lot then maybe hold the salt and use the Stresscoat instead.

As for the spray, particles float about so if you dont have a tight seal and/or cover around your tank and equipment then moving it might help prevent anything from causing an issue.

I do have two more things to add after seeing the photos:
-Use that quick start if you havent been already, follow the directions as if you're starting up a tank because we cant rule out a mini-cycle. I do agree with A201, this seems to be one of those wait-and-see type of things now that you're seeing more activity in your corys.
-I would recommend a more carnivorous wafer for your common pleco soon if not now. They only eat algae when they're tiny but quickly switch to a need for meaty protein to support their growing size. And you may need to eventually consider rehoming it as they get incredibly huge. I used to have x3 18-22" long ones in my pond, had to rehome them as they eventually started attacking the koi. Not that i can blame them as Im sure the koi would eat their food, but I mean it is a koi pond not a common pleco pond.

 

Hard to say with city water, lots of things can happen whether it's treatment or something in pipes. Even more reason to make sure you have good water conditioner. Which, I think nowadays a little more than the recommended dose of your water conditioner should be harmless. If you spill half a bottle in a tank then that would be different, but I dont think being slightly off with measurement will cause any harm.

KH is definitely an advanced topic in fishkeeping, at least on the water chemistry side of things. I can't consider myself an expert on this topic, as it hasnt been too relevant to my personal tanks. It is rarely if ever mentioned to beginners and on many blogs and websites for keeping aquariums that only share mostly basic information. It only becomes a little more important to know if you plan to keep fish have unique requirements in their water. Like certain rift lake cichlids of Africa prefer high pH and very hardwater, or many south american species that might prefer much more acidic conditions. If there is anything you should take away about kH here, it influences pH. If you have hardwater deposits then you probably have some decent kH that should in theory keep your pH stable. But city water can be weird sometimes...

Salt is pretty handy in the hobby but I personally recommend situational use. Above all else, be sure that when you use it that it is completely diluted in some tank water before you put it into the tank. The salt crystals can be irritating to bottom feeders that come across it, especially any scaleless fish like loaches. It can be useful as a non-medicated treatment against external parasites and infections, however with regular use of salt it could potentially make a salt treatment less effective, a tolerance can be built by external parasites and such. Salt is supposed to stimulate fish into producing a thicker slime coat around their body, and this is supposed to help them better fight off any potential infections while theyre stressed. API Stresscoat does this and helps condition the water as well, but I think with a less irritating ingredient than salt (aloe I think?). If your fish get stressed a lot then maybe hold the salt and use the Stresscoat instead.

As for the spray, particles float about so if you dont have a tight seal and/or cover around your tank and equipment then moving it might help prevent anything from causing an issue.

I do have two more things to add after seeing the photos:
-Use that quick start if you havent been already, follow the directions as if you're starting up a tank because we cant rule out a mini-cycle. I do agree with A201, this seems to be one of those wait-and-see type of things now that you're seeing more activity in your corys.
-I would recommend a more carnivorous wafer for your common pleco soon if not now. They only eat algae when they're tiny but quickly switch to a need for meaty protein to support their growing size. And you may need to eventually consider rehoming it as they get incredibly huge. I used to have x3 18-22" long ones in my pond, had to rehome them as they eventually started attacking the koi. Not that i can blame them as Im sure the koi would eat their food, but I mean it is a koi pond not a common pleco pond.

Yes, I feed the pleco the shrimp bottom feeder pellets, and now I’m having a “brown algae bloom”, I’m gonna let that play it’s corse. I lost another Cory, they’re still for the most part staying still but I’m sure they are eating at least the bare minimum or they probably would have died by now, the pleco will be rehomed soon to a lfs as they have the required tank for him, I was told he was a bristlenose when I bought him from a PetSmart as to why I don’t buy fish from them places anymore, he was smaller then a quarter when I got him now he’s pushing 6”, I’ve enjoyed watching him grow and don’t wanna get rid of him but I can’t afford to buy a bigger tank for him, and the rest of my fish are a lot smaller, but I retested my ph today and it is now over 8? Kinda scared me but all other tests came out perfect